Thats only because none of the current big stars (With the exception of Bey) are vocalists. The same thing happened in the early eighties when everything was dance music and Madonna was the biggest new artist, but then Whitney Houston came along in 1985 and made vocals popular again. All we need is for a huge new vocalist to break through, in fact I think Adele may already have changed the industry a little but its not enough.
Xtina, but I wouldn't really class her as just a pop vocalist as she is beyond this and the world renowned voice of the generation, but that being said....